The most common cause of Parathyroid Hormone (PTH) deficiency is hypoparathyroidism. This condition arises when the parathyroid glands are unable to produce or secrete sufficient levels of PTH. Key factors contributing to hypoparathyroidism include damage to the parathyroid glands (e.g., after surgical intervention), radiotherapy, and severe magnesium deficiency. Hypoparathyroidism is generally a manageable condition, and with appropriate treatment, serious health complications can be prevented.